1. Field of the Invention
The present invention relates to an electronic still camera system which compensate for an image shift between two field images, which are field-sequentially obtained by electronically imaging an object image, when the two filed images are synthesized into a frame image, thereby obtaining a clear frame image.
2. Description of the Related Art
Recently, in place of a camera using a silver salt film, a great deal of attention has been paid to a solid-state imaging device called an electronic still camera, which records an electronic still image signal obtained by an electronic imaging operation using a solid-state imaging element such as a CCD (charge coupled device), and provides the recorded image for image display by means of a TV monitor or the like. According to an electronic still camera of this type, unlike a photographing operation using a silver salt film, a photographed image (still image) can be easily monitored without performing film development, printing, and the like, and the obtained image can be directly transmitted as image data to be used in the field of news media or the like.
There are two schemes for electronically imaging an object image by using a solid-state imaging element: a scheme for directly obtaining one frame image, provided for image reproduction (display) by means of a TV monitor, from the solid-state imaging element; and a scheme for field-sequentially obtaining two field images (odd and even field images provided for image reproduction by means of a TV monitor) from the solid-state imaging element. In the scheme for field-sequentially obtaining two field images, an electronic still image (frame image) is formed by substantially increasing the number of pixels twice that in the scheme for directly obtaining a frame image from the solid-state imaging element. Therefore, the pixels of the solid-state imaging element can be effectively used to obtain a high-resolution, high-quality electronic still image.
When, however, two field images are field-sequentially obtained from the solid-state imaging element, it is inevitable that the imaging timings of these field images slightly differ from each other. In general, such a difference in timing tends to cause a shift of an object image between two field images (hereinafter referred to an inter-field movement). Especially when a moving object is to be imaged, a shift of an image becomes conspicuous.
Such an image shift between field images poses almost no problem in motion pictures. In electronic still images, however, since these two field images are repeatedly and alternately reproduced and output to perform frame image display, an image shift tends to appear as so-called flicker. Such flicker disturbs a display image and causes a deterioration in quality of a reproduced frame image. In addition, when a still image is to be printed, the inter-field movement causes blurring of an image and hence deteriorates sharpness of the image. Such a problem is similarly posed when still image reproduction is performed in a movie camera. Furthermore, the same problem is posed in a camera using an imaging tube as well as a camera using a solid-state imaging element, such as a CCD, as an imaging portion.